The present invention relates to a reel spring of a magnetic tape cassette for forcing in a direction to a reel around which a magnetic tape is wound and which is rotatably provided in a cassette case. The present invention also relates to a magnetic tape cassette using the reel spring.
In audio set equipment, video set equipment or the like, a magnetic tape cassette which allows a magnetic tape wound around a pair of reels to run in a cassette case to perform recording and replaying has generally been used.
In such magnetic tape cassette, a pair of reel springs are provided in the cassette case to prevent the pair of reels around which a magnetic tape is wound from displacing in an axial direction of rotation and to allow the tape to run smoothly whereupon the pair of reels are forced on in the axial direction of rotation in the cassette case by the pair of reel springs each other.
FIG. 3 shows a part of a digital video cassette L type (DVC-L) as a digital video cassette for business use which has such reel springs.
As shown in FIG. 3, the digital video cassette 30 comprises an upper half 32 of a cassette case, a pair of reels 34 around which a magnetic tape is wound and which are rotatably provided in the cassette case and a pair of reel springs which are each a flat plate in an approximately rectangular shape having a bending portion in a midway in a longitudinal direction to form an L-like shape, as well as other members not shown in the figure such as a lower half as a part of the cassette case, an outer lid, an upper lid and an inner lid which constitute a lid to cover an opening in the front of the cassette case, various springs and the like.
The reel spring 36, as shown in FIGS. 4A and 4B, has a fixing portion 36a which is fixed to the cassette case to form a fixing end, an arm portion 36b which forces on the aforementioned reel in the axial direction of rotation and a bending portion 36c provided between the fixing portion 36a and the arm portion 36b. 
The fixing portion 36a has a boss hole 46. The boss hole 46 is provided so as to fix the reel spring 36 to a reel spring provision portion 40 which is provided in the upper half 32 of the cassette case shown in FIG. 3.
An end of the reel spring 36 is chamfered off in a triangular shape and the other end thereof in a circular shape.
A length of the arm portion 36b, namely a length from the bending portion 36c to an edge of the arm portion 36b, is needed to be long within an extent enough for keeping an urging force consistently, for reducing variation of the urging force by device of a variation of dimension of the reel spring 36 inherent to mass production of reel spring 36 which forces a reel 34 with a specified urging force, exemplified by a variation of bending angel of bending portion 36c. 
Moreover, ratio of a length of the fixing portion 36a, which is defined by a length from the bending portion 36c to an edge of the fixing portion 36a, to the length of the arm portion 36a is preferred to be larger within an extent enough for keeping the specified urging force consistently, though not necessarily being over 1.0, because of preventing the fixing portion 36a which should be in contact with a bottom surface of the upper half 32 from being deformed and partially lifted when the reel spring 36 forces on the reel 34, as shown in FIG. 5. Therefore, the length of the arm portion 36b is designed to be longer than that of the fixing portion 36a, for example 5 mm longer.
The diameter of the boss hole 46 of the fixing portion 36a is formed larger than that of an upper half boss 42 so that, when the reel spring 36 is provided to a reel spring provision portion 40, it gets regulated in a lateral direction by reel spring provision portion guides 44 and the reel spring is easily engaged with the upper half boss 42 of the upper half 32.
When the digital video cassette 30 is assembled, such reel spring 36 is provided to the reel spring provision portion 40 of the upper half 32 by reel spring supply device not shown in the figure, is regulated in the lateral direction by reel spring provision portion guides 44 and mounted in a manner that the boss hole 46 is engaged with the upper half boss 42 on the upper half 32. Thereafter, the reel spring 36 is transported to a welding step of a cassette assembly line in which a top of the upper half boss 42 engaged with the boss hole 46 of the reel spring 36 is melted and the reel spring is welded to the upper half 32.
In this occasion, as described above, in order to prevent the fixing portion 36a of the reel spring 36 welded to the upper half 32 from being deformed and partially lifted from the bottom surface of the reel spring provision portion 40 (see FIG. 5), the length of the arm portion 36b is designed longer than that of the fixing portion 36a so that the arm portion 36b contacts the bottom surface of the reel spring provision portion 40 in relation with a position of the gravity center and, accordingly, the fixing portion 36a comes to be in a lifted state. However, in a case in which the digital video cassette is a small-sized one for private use (DVC-S type) where a ratio of the length of the fixing portion 36a to a height of the upper half boss 42 is less than 4.0, as shown in FIG. 6, the boss hole 46 of the fixing portion 36a is not released (disengaged) from the upper half boss 42 of the upper half 32 so that problems such as complexity of welding operation or of transportation operation, decrease of assembling work efficiency and so forth do not occur.
In contrast, in another case in which the digital video cassette is a large-sized one for business use where the ratio is 4.0 or more as L type (DVC-L), the reel spring 36 should be longer longitudinally in accordance with the size of the digital video cassette and. As a result, when the length of the reel spring 36 comes to be longer, the length of the arm portion 36b, as well as that of the fixing portion 36a, becomes longer even if the ratio of the arm portion 36b to the fixing portion 36 and the bending angle of the bending portion 36c are not changed so that, even when the fixing portion 36a of the reel spring 36 is mounted on the reel spring provision portion 40 in a manner that the upper half boss 46 of the upper half 32 is engaged with the boss hole 46 of the reel spring 36, as shown in FIG. 7, the boss hole 46 of the fixing portion 36a is likely to be released from the upper half boss 42 on the upper half 32. Therefore, during the transportation to the welding step, instead of being laterally regulated with the reel spring provision portion guides 44, the reel spring 36 bounces or slides in a disposal direction either of the right or left ridge of the reel spring provision portion guides 44, by vibration or the like to be dislocated from the appropriate position. Moreover, a trouble occurs in a welding operation in that, at the time of welding, the welding operation must be performed by pressing the fixing portion 36a down to the bottom surface of the reel spring provision portion 40 so that it may not be lifted up.
To cope with these problems, it is conceivable to provide a device to press down the reel spring 36 so that the reel spring 36 may not be dislocated from the reel spring provision portion 40 during the transportation. However, this causes transportation operation complicate.
Even if the device which presses down the reel spring 36 is provided during the transportation to allow the reel spring 36 to remain in an appropriate position, it is necessary to weld the upper half boss 42 with an ultrasonic welder or the like while keeping the reel spring 36 in a specified set condition preventing the fixing portion 36a from being lifted up at the welding step. This causes to complicate welding step as well as welding operation at the welding step thereby leading to decrease of an assembly efficiency.
It is also conceivable that the height of the upper half boss 42 is designed to be increased; however, if the height of the upper half boss 42 is increased, welding volume needed for fixing the reel spring 36 to the upper half boss 42 is increased whereupon welding time becomes longer, which leads to decrease of an efficiency of welding process.
It is also conceivable that the length of the fixing portion 36a is designed to be decreased to an extent that the boss hole 46 is not released from the upper half boss 42 on the upper half 32; however, the length of the arm portion 36b is so long that the reel spring 36 can not obtain a specified force acting on the reel 34.
Its is further conceivable that the bending angle of the bending portion 36c of the reel spring 36 is brought to be shorter; however, the same problem as the above occurs.
Accordingly, it is an object of the present invention to solve the aforementioned problems and to provide a reel spring of a magnetic tape cassette having the ratio of a length of fixing portion to a height of an upper half boss being 4.0 or more and a magnetic tape cassette using the reel spring, wherein, when the reel spring is supplied to a cassette case, transported and welded during the assembly of the magnetic tape cassette, the reel spring can not be dislocated from an appropriate position in the cassette case, solves the complexity occurring at the welding step of the reel spring and can improve production efficiency over the prior art.
The present invention provides a reel spring for use of a magnetic tape cassette having a cassette case and a pair of reels wound with a magnetic tape and rotatably provided in the cassette case, the reel spring for forcing one of the pair of reels in an axial direction of rotation, comprising:
a fixing portion for being fixed to the cassette case, the fixing portion having a boss hole for being engaged to a boss of the cassette case;
an arm portion which forces on the one of the reels in the axial direction of rotation; and
a bending portion to form an L-like shape provided between the fixing portion and the arm portion,
wherein a ratio of a length of the fixing portion to a height of the boss is equal to or more than 4.0, and
wherein the length of the fixing portion is longer than a length of the arm portion by from 1 mm to 5 mm.
It is preferable that the length of the fixing portion is longer than that of the arm portion by from 2 mm to 3 mm.
It is preferable that a position of gravity center of the reel spring is positioned at least in a region of the fixing portion from the bending portion as a border.
It is preferable that at lease one of ends of the fixing portion and the arm portion is chamfered off.
It is preferable that the reel spring is employed in a pair, and each reel spring of the pair forces each of the pair of reels.
The present invention also provides a magnetic tape cassette, comprising:
a cassette case;
a pair of reels wound with a magnetic tape and rotatably provided in the cassette case; and
a pair of reel springs disposed to the cassette case for forcing each of the pair of reels in an axial direction of rotation, the cassette case having a pair of bosses for disposal of the pair of reel springs, each of the pair of reel springs comprising:
a fixing portion for being fixed to the cassette case, the fixing portion having a boss hole for being engaged to one of the pair of bosses of the cassette case to form an fixing end when it is fixed to the cassette case;
an arm portion for forcing on each of the reels in the axial direction of rotation; and
a bending portion to form an L-like shape provided between the fixing portion and the arm portion,
wherein a ratio of a length of the fixing portion to a height of the boss is equal to or more than 4.0, and
wherein the length of the fixing portion is longer than a length of the arm portion by from 1 mm to 5 mm.